CCELENTERATA — CORALS 



133 



The corallites are thick-walled with well-developed tabulae. 

 The polyp occupied only the space above the last-formed tabula. 



A 



B 



Fig. 50. — Columnaria alveolata Goldfusis, an abundant coral in the Ordovician seas 

 which covered most of the present area of the North American continent. A, 

 transverse section ( X 2I) through eleven entire individuals; B, longitudinal 

 section of three of the individuals, s., septa ; /., tabulae. (From Lambe.) 



It is much like Favosites, but without mural pores and with 

 septa well developed or present as vertical ridges. 



1. Sketch a group of three or four corallites, showing both 

 sides and top ; grind one corallite down until it shows the tabulae. 

 Label corallites, septa, tabulae. 



2. Did a single or several polyps secrete the corallites 

 sketched ? Reasons. 



3. How did the polyp form the septa ? the tabulae ? 



4. Outline a polyp upon your above sketch. 



Super -order b, Hexacoralla 



Simple or composite corals with septa in cycles of six or mul- 

 tiples of six (whence the name from Greek hex, six). Corallum 

 calcareous, horny or fleshy. Here are included the reef-build- 

 ing and deep-sea corals of to-day. The Hexacoralla are abun- 

 dant from the Triassic to the present. The few Paleozoic 

 (Silurian-Permian) forms referred to the Hexacoralla may belong 

 to the Tetracoralla. 



The living sea anemones belong here likewise. These pos- 



